igneous
Scoria (Vesicular Basalt)
Scoria (Extrusive Igneous Rock)
Hardness: 5-6 (Mohs scale); Color: Dark brown, black, or reddish-brown; Luster: Dull/Earthy; Crystal Structure: Aphanitic (fine-grained) with large vesicles (gas bubbles); Cleavage: None; Specific Gravity: 0.8 - 2.1 (relatively light due to air pockets).
- Hardness
- 5-6 (Mohs scale)
- Color
- Dark brown, black, or reddish-brown
- Luster
- Dull/Earthy
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Physical properties
Hardness: 5-6 (Mohs scale); Color: Dark brown, black, or reddish-brown; Luster: Dull/Earthy; Crystal Structure: Aphanitic (fine-grained) with large vesicles (gas bubbles); Cleavage: None; Specific Gravity: 0.8 - 2.1 (relatively light due to air pockets).
Formation & geological history
Formed from the rapid cooling of basaltic or andesitic lava containing high amounts of dissolved gases. As the magma erupts, gases expand and escape, leaving behind a 'frozen' foam of holes. Geologically common from the Cenozoic era to the present in volcanic fields.
Uses & applications
Commonly used in landscaping (lava rock), high-temperature insulation, lightweight concrete aggregate, traction on snow-covered roads, and gas grill heat retention.
Geological facts
Scoria is often confused with pumice, but scoria is more dense and sinks in water, whereas pumice typically floats. It is a primary component of cinder cones, which are the simplest type of volcano.
Field identification & locations
Identify by its 'Swiss cheese' appearance, rough/abrasive texture, and dark color. It is commonly found around volcanic vents and cinder cones. In the field, look for a lightweight, jagged rock that feels like sandpaper.
